This invention relates to a means for straightening and locking a cantilevered mold core into desired molding alignment before injecting a molding composition into a cavity for a deep, thin-walled container. The invention is particularly adapted for injection molding rigid, thin-walled, partitioned containers such as multi-cell battery cases for automotive applications.
Relatively deep, thin-walled containers may be injection molded by inserting one or more elongated, cantilevered cores into a female mold and injecting a hardenable polymeric material into the mold cavity formed between them. A partitioned container may be formed by inserting a plurality of cores into a female mold, the spaces between cores defining the partition walls. Generally, polypropylene cases for multi-celled automotive storage battery cases are made in this manner.
Unless elongated mold cores are restrained at their free ends during the initial high pressure injection of the molding material, they tend to become misaligned with respect to one another. Any deflection of the cores out of desired alignment causes variations in partition and outer wall thicknesses. If the cores are greatly misaligned, the partitioned walls will be uneven and improperly spaced. Even slight variations in container wall thicknesses make ejection of a finished part difficult and tend to increase mold residence time. Thus it has been desired to provide a means and method for locking mold cores into position for the high pressure injection of molding material. Means have also been sought for straightening cores which have been bent out of alignment.
In the molding of multicelled automotive battery cases, one method of restraining mold cores has been the insertion of retractable pins into complementary recesses in the free ends of the cores prior to material injection. The pins are retracted near the end of the material injection portion of the molding cycle. The pin retraction causes the pin recesses in the cores to fill with the molding composition. This creates undesirable peg-like projections into the bottoms of the molded container. Moreover, this locking system will not tolerate bent cores. Any misalignment between the cores and the pins before mold closure may cause the pins to break or bend leading to expensive mold repair and machine down time.
Another method has been the insertion of pie shaped wedges between the free ends of adjacent cores prior to material injection. The wedges are retracted near the end of the material injection portion of the molding cycle to fill out the bottom of the battery case. This method produces sloping surfaces between partition walls and the bottom of the battery case. These slanted portions may interfere with the later insertion of battery plates into cell compartments. This method also requires the use of special holders for the end cores adjacent the battery case end walls so that they will not be bent out of alignment. This severely complicates the mold adding to initial expense and mold maintenance.
It is therefore an object of this invention to provide an improved apparatus for injection molding deep, thin-walled containers wherein elongated cantilevered core members are straightened and locked into position prior to injecting a molding material. Another object is to provide means for straightening and locking cantilevered cores for injection molding wherein a core locking cam means is rotatably retained in the mold base and complementary cam reacting means are located in the free ends of the cores. Means are further provided to rotate the core locking cam means with respect to the cores to force them into desired alignment and lock them into such alignment before injecting a hardenable molding material. A more specific object is to provide at least one cam-type locking member for each cantilevered core member and means to telescope the cam locking member into and out of the free end of a mold core. Another object is to provide means to rotate the locking members with respect to the cores to provide a cam-type straightening and locking thereof preparatory to molding.
A more specific object of the invention is to provide an improved molding apparatus for injection molding thin-walled containers which are divided into compartments by integral thin partitioning walls. It is an object to provide such apparatus with means for simultaneously locking a plurality of core members into parallel alignment prior to molding so that the wall defining portions of the mold cavity formed between the cores are of uniform thickness.
Another object of the invention is to provide apparatus for making deep, thin-walled containers where specially adapted cam-type locking members are provided in the base of the mold. It is a further object to provide means to sequentially insert these members into cooperative receiving members at the free ends of the cantilevered mold cores; to rotate the locking members within the receiving members to bring the cores into desired molding alignment and lock them prior to injecting molding material; to rotate the locking members out of locking engagement after material is injected into the mold; and to withdraw them from the core members to provide for fill-out of the container wall between the base and core ends. A more specific object of the invention is to provide locking means in the base of the mold in the form of noncircular or ellipsoidal protruding cams and complementary shaped receiving portions in the free ends of the core which are lockingly engageable by the cams.
Another object of the invention is to provide an improved apparatus for molding deep, thin-walled containers by locking elongated mold core members into position prior to injecting a hardenable molding material. A more particular object of the apparatus is to telescope a cam-type core locking member (retained in the bottom of the mold) into a corresponding receiving member (located in the free end of the core) and to rotate the locking member relative to the receiving member so that the end of the core is cammed and straightened into the desired alignment and locked prior to injecting the molding material.